Control means for maintaining design pressure upon the capillary tube of a refrigeration system



March 15, 1955 s F. SHAWHAN 2,703,965

CONTROL MEANS FOR MAINTAINING DESIGN PRESSURE UPON THE CAPILLARY TUBE OF A REFRIGERATION SYSTEM Filed Aug. 18 1951 INVENTOR. PM BY 4L United States Patent CONTROL MEANS FOR MAINTAINING DESIGN PRESSURE UPON THE CAPILLARY TUBE OF A REFRIGERATION SYSTEM Sam F. Shawhan, Syracuse, N. Y., assignor to Carrier Corporation, Syracuse, N. Y., a corporation of Delaware Application August 18, 1951, Serial No. 242,506

4 Claims. (Cl. 62-3) This invention relates to control means for refrigeration systems including a capillary tube and more particularly to mechanism for maintaining design pressure upon the capillary tube of a refrigeration system.

The use of capillary tubes in refrigeration systems is advantageous due to their simplicity and to the fact that no moving parts are required. Capillary tubes, however, possess the disadvantage that a loss of capacity ensues whenever the refrigeration system is operated under other than design conditions. This is due, of course, to the fact that there are only a certain set of suction pressures and discharge pressures under which any particular capillary tube will not pass gas or will not permit liquid to back up into the condenser.

The chief object of the present invention is to provide a refrigeration system employing a capillary tube to meter refrigerant passing to the evaporator in which indirect control of the capillary tube is effected permitting it to operate satisfactorily at other than design conditions.

An object of the present invention is to provide a refrigeration system including a liquid condenser and employing a capillary tube or other restriction to meter refrigerant passing to the evaporator in which flow of cooling liquid through the condenser is regulated in response to change in superheat in the suction line thereby maintaining a discharge pressure upon the capillary tube substantially equivalent to the pressure thereon which exists under design conditions. Other objects of my invention will be readily perceived from the following description:

This invention relates to a refrigeration system comprising, in combination, a compressor, a liquid cooled condenser, a restriction, an evaporator and a suction line connecting the evaporator with the compressor, means to supply cooling liquid to the condenser, and means to regulate supply of cooling liquid to the condenser responsive to superheat in the suction line.

This invention further relates to a method of operation of a refrigeration system including a capillary tube to regulate flow of refrigerant to the evaporator and a liquid cooled condenser, in which the steps consist in condensing gaseous refrigerant by passing the gaseous refrigerant in heat exchange relation with a cooling liquid, and varying the flow of cooling liquid responsive to change in superheat in the suction line of the refrigeration system.

The attached drawing is a diagrammatic view of a re frigeration system embodying the present invention.

Referring to the drawing, there is shown schematically a refrigeration system embodying the present invention. The refrigeration system includes a compressor 2 connected by line 3 to a liquid cooled condenser 4. The condenser 4 may be the usual two shell type or as shown it may consist of a container 5 containing a coil 6 connected to line 7 leading to the source of supply of a liquid such as water and to line 8 which in turn is connected to a cooling tower or waste as desired. I Preferably, condenser 4 is connected to receiver 9. Receiver 9 is connected in turn by liquid line 10 and capillary tube 11 to an evaporator 12. Evaporator 12 is connected to compressor 2 by suction line 13.

Passage of cooling liquid through coil 6 of condenser 4 is regulated by valve 14 placed in supply line 7. An equalizer line connects the valve to the suction line. Valve 14 contains a diaphragm or bellows (not shown) and is connected by capillary 15 to a bulb 16 placed in contact with suction line 13. The bulb, bellows and capillary contain a thermal responsive fill as is well known in the industry so that an increase or decrease in temperature in the suction line is reflected by an increase or decrease in the pressure applied against the diaphragm or bellows of valve 14 thereby moving the valve toward an open position or toward a closed position to increase or to decrease flow of cooling liquid through the condenser.

Considering the operation of the refrigeration system, capillary tube 11 regulates or meters the flow of liquid refrigerant to evaporator 12. As described above, there are only a certain set of suction and discharge pressures at which the capillary tube will permit the system to operate without loss of capacity. Assuming an increase in load imposed upon the evaporator, temperature of refrigerant in the suction line will increase. Under ordinary circumstances, with increased load the capillary tube 11 will pass insuflicient refrigerant to the evaporator with a resulting loss of capacity. In accordance with the present invention, however, the increase in pressure and superheat in suction line 13 is reflected by bulb 16 which actuates valve 14 to move toward a closed position decreasing the flow of cooling liquid; through the condenser thus maintaining the desired pressure across capillary 11 and permitting the capillary to pass liquid refrigerant required to fill evaporator coil.

Likewise, upon a decrease in pressure and temperature in the suction line occasioned by a decrease in the load imposed upon the evaporator, such decrease is reflected by bulb 16 which actuates valve 14 to move toward an open position, increasing the flow of cooling liquid through the condenser so as to maintain the desired pressure upon capillary 11 to fill evaporator coil.

The present invention providesfa simple, economical indirect control for a refrigeration system having a water cooled condenser and employing an inexpensive capillary tube to meter flow of liquid refrigerant to the evaporator. The control so provided is automatic and assures that design pressure is maintained on thei capillary tube regardless of change in load on the system thereby preventing passage of gaseous refrigerant to the evaporator or liquid refrigerant backing up into thecogidenser upon a change in load. While I have described a preferred embodiment of the invention, it will beffunderstood the invention is not limited thereto since it"fmay be otherwise embodied within the scope of the following claims.

I claim:

1. In a refrigeration system, the-combination of a compressor, a liquid cooled condenserif'a capillary, an evaporator and a suction line connecting the evaporator with the compressor, means to supplyf -cooling liquid to the condenser, and control means to decrease the supply of cooling liquid to the condenser responsive to an increase n the amount of superheat in the. suction line and to increase the supply of liquid to the-"condenser responsive lt o a decrease in the amount of superheat in the suction 2. In a refrigeration system, the combination of a compressor, a liquid cooled condenser, a capillary tube, an evaporator and a suction line connecting the evaporator with the compressor, a supply line through which cooling liquid is supplied to the condenser, and valve means in the supply line for varying the discharge pressure on said capillary tube in accordance with the load on the evaporator as evidenced by the amount of superheat in the suction line, by increasing the flow of the cooling liquid to the condenser when the superheat is decreased and by decreasing the flow of the cooling liquid to the condenser when the superheat is increased.

3. A refrigeration system according to claim 2 in which the valve is actuated by a thermal responsive system including a bulb placed in contact with the suction line to reflect superheat in the suction line.

4. In the method of operation of a refrigeration system including a capillary tube to regulate .fiow of refrigerant to the evaporator and a liquid cooled condenser, the steps which consist in condensing gaseous refrigerant by passing the gaseous refrigerant in heat exchange relation with a cooling liquid, and inversely varying the flow of cooling liquid responsive to change in superheat in the suction line of the refrigeration system so as to maintain 1,726,791 Andrews Sept. 3, 1929 a desired pressure on the capillary tube. 1,860,447 Bergdoll May 31, 1932 2,171,239 Gygax Aug. 29, 1939 References Cited in the file of this patent UNITED STATES PATENTS 1,148,464 Sayer July 27, 1915 

